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Unread 07-04-2008, 07:51 PM   #1
Zappy
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Drop in average mpg of 3.5 mpg...

This has me a little perplexed to say the least. I bought this 2007 Compass Limited 4X4 back in early March. It has the CV2 autostick feature and came with just under 25K miles on it. Up until the last 3-4 weeks I was averaging between 24.3 - 24.7 mpg with every tank of gas.

I have not changed my driving habits, or route to work. The tire pressure is right where it has been at 35psi when cold with no uneven wear to the tread noted. I have changed the oil (going to amsoil full synthetic), changed the air filter and the spark plugs to the Iridium plugs referenced in THIS thread and verified the gap was correct on all the plugs. This was all done prior to the drop being noted. Yet, instead of those things either helping to maintain or improve my mileage, for some reason it's slipped down to roughly 21.3mpg the last few tanks now.

I have even thought it may be the gas, so each fill up I've tried to hit a different gas station, but no luck in getting it back up where it was. I'm not getting any warning lights indicating any issues with the engine and when I am at a complete stop at a red light, it's still idling so smoothly that I can hardly hear or feel it.

Does anyone have any idea as to what may have so suddenly caused that drop? With the price of gas being what it is and the amount of driving I do (In the 4 months I've owned it I've put over 6K miles on it) every little bit adds up quick in the wallet. Any ideas, suggestions or comments are appreciated.

And yes, if I can't come up with anything I'll try to find a day when I can get it to a dealer to check it out to see if they come up with anything. Thanks.

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Unread 07-04-2008, 10:21 PM   #2
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Not a clue. I've changed the wife's GC over to Amsoil with an air filter and she's seen about .5 mpg improvement just on the next tank full. I'll be doing mine sone with plugs too and I'll see what happens with it.
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Unread 07-05-2008, 07:35 AM   #3
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Thanks Gramps. I'm glad that I'm not the only one that's at a loss to figure out whats going on here. With the engine sounding and running and smooth, my concern is that it might be something with the transmission going on that's not blatantly obvious at the moment. With the CVT, it's hard to really get a feel for how its shifting when I've gotten so used to the 'normal' automatic transmissions where you can both hear and feel the shift points and how smoothly they transition.
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Unread 07-05-2008, 08:07 PM   #4
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Does it roll smoothly when in neutral. (A dragging brake can cause behavior like you are describing...)

You might want to check the air filter and tire pressure. Lower tire pressure can really eat gas.

Other than that..??? No clue..
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Unread 07-07-2008, 08:50 AM   #5
Zappy
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I checked on the way into work today and it rolls very smoothly when in neutral. The air filter was recently changed and still looks brand new and is firmly locked in its enclosure. Tire pressure is still right at 35psi for all four tires when cold, which is what it has been for the last 3 months.

I know...its a head scratcher....
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Unread 07-07-2008, 05:36 PM   #6
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Since its getting hotter, are you running A/C??? I was getting 35 MPG last night on my way to T-Town, but after running around town today, its sadly down to 28.5 again... I HATE traffic lights and morons...
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Unread 07-09-2008, 05:53 AM   #7
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I had thought of that as well and have tried running the last several days with no a/c running and just the normal fan blowing for air circulation and have not been able to notice any difference at all in the mileage.

Do I have to do anything other then just disconnect the negative cable to the battery for several minutes to reset the chips that regulate the engine? That's my next idea and if that doesnt do anything, I'm going to have to try figure out a time when I get it into the dealer for a more thorough check.

The only thing that was done just before these problems was the plugs being changed over to the Iridium plugs mentioned in my first post. I verified the gaps were correct and they were all seated properly and reconnected correctly. I may get a set of secondary oem plugs and install them this weekend just to see if there is a difference.

Thanks for the continued help and ideas everyone.
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Unread 07-09-2008, 06:23 AM   #8
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My understanding is that disconnecting the battery for an hour (may actually be less) will reset the computer. I'm curious as to how the spark plug swap will effect it too.
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Unread 07-09-2008, 12:58 PM   #9
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Kinda different -but maybe not

I have been very disappointed with my mileage for the last 1.5-2 years. So I have been making a conscious effort to improve it -when something very strange happened this morning. But first for some background;
When I first got my jeep I was getting 16.6 - 18 MPG. This dropped off pretty quickly due to a lot of always in a rush city driving. My mileage (averaged) went as low as 9.8 - ~ 11. I changed the breather and plugs and ran some injector cleaner through and (most of all) changed my driving habits, for the last 6 months or so. I have seen a marked increase in mileage and was up to 14.9 -by keeping it at 70 and below using cruise when possible, slow starts and not speeding like there was a fire -unless I actually was responding to one.
Now this morning something strange happened. I keyed the ignition and there was nothing, no click, nothing I looked at the dash before releasing the key from start and I saw the gauges go through 2 test cycles -as if you were retrieving diags from the computer. Once I released and re-keyed the ignition it started fine without hesitation. Now my avg. MPG is saying I am getting about 18-19MPG (I have only taken it about 15 miles to work since this happened). I thought the car lost power (the battery is fine 10mos old and holding and charging normally) but it did not because my radio presets, clock, and elapsed time and trip since last fill are not reset.
It appears my computer (which was flashed with the latest software by the dealer last year) reset.
Has anyone ever heard of this happening? it just seemed strange and thought I’d share.
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Unread 07-09-2008, 03:27 PM   #10
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I have NOT heard of mileage that bad on an MK or Caliber, not even the SRTs get that terrible... My Wrangler 2.5L gets better than that...
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Unread 07-09-2008, 05:43 PM   #11
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Quote:
Originally Posted by pulls2theright View Post
I have been very disappointed with my mileage for the last 1.5-2 years. So I have been making a conscious effort to improve it -when something very strange happened this morning. But first for some background;
When I first got my jeep I was getting 16.6 - 18 MPG. This dropped off pretty quickly due to a lot of always in a rush city driving. My mileage (averaged) went as low as 9.8 - ~ 11. I changed the breather and plugs and ran some injector cleaner through and (most of all) changed my driving habits, for the last 6 months or so. I have seen a marked increase in mileage and was up to 14.9 -by keeping it at 70 and below using cruise when possible, slow starts and not speeding like there was a fire -unless I actually was responding to one.
Now this morning something strange happened. I keyed the ignition and there was nothing, no click, nothing I looked at the dash before releasing the key from start and I saw the gauges go through 2 test cycles -as if you were retrieving diags from the computer. Once I released and re-keyed the ignition it started fine without hesitation. Now my avg. MPG is saying I am getting about 18-19MPG (I have only taken it about 15 miles to work since this happened). I thought the car lost power (the battery is fine 10mos old and holding and charging normally) but it did not because my radio presets, clock, and elapsed time and trip since last fill are not reset.
It appears my computer (which was flashed with the latest software by the dealer last year) reset.
Has anyone ever heard of this happening? it just seemed strange and thought I’d share.
You may want to cruise over to the WJ area and see if there is something over there, not that you're not welcome over here. It does sound like your computer had indigestion or something. You may also want to go here and get the Diagnostic codes and see if anything comes up and here where there is lots of info on the WJ's.

My wife has had her '03 WJ for about a year now and we just switched her over to Amsoil and I'm still doing mileage tests on it to see what the change has been. Hers is the 4.0 and she's getting about 18.5 which is better than the Daughter's V-6 Libby at about 17mpg.
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Unread 07-18-2008, 08:28 AM   #12
Zappy
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Sorry for lack of updates. No new news yet regarding this and no change in the overall status of the problem. Haven't had the time to try resetting the computer yet or getting a new set of plugs. Will probably tackle both of those issues next weekend rather then this coming weekend. Sometimes I wonder where the time goes.....
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Unread 07-20-2008, 11:00 AM   #13
Zappy
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I think we may have figured it out. Based on information in this topic I think the problem stemmed from my not disconnecting the negative terminal from the battery when I changed my spark plugs.

Yesterday I disconnect the negative terminal and let the jeep sit for an hour or so before hooking it back up. I then made the 50 mile round trip into work and back and my mileage average went from 21.7 to 26.2 which is pretty good considering all of the hills around here. One day is too soon to be absolutely sure that's what the problem was, but it sure seems like that's what it was so far.

Thanks again for all the suggestions folks, it really is appreciated. I'll let you know how the rest of tank of gas averages out.
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Unread 07-20-2008, 11:15 AM   #14
Gramps
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Thanks for the follow up! Some things sound so silly until you don't do them and then things go wrong. Who'd a thunk that one.
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MK Skid Plate fasteners for sale posts 68 & 69

Also visit me at Photobucket
'06 WK Grand Cherokee Limited Quadra-Drive II, 5.7
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Unread 07-20-2008, 11:22 AM   #15
Zappy
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I know... I have never had to disconnect a battery when changing plugs before... Live and learn.
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